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I have the following example files

docker-compose.yml

version: '3' services: web: image: webapp:${VARIABLE_A:-${VARIABLE_B}}

env.conf

VARIABLE_B=123

VARIABLE_A is not set on purpose so it should fall back to VARIABLE_B

Docker compose is able to resolve the default value of the environment variable, however docker stack deploy is unable to do the same resolution

user@laptop:~$ docker compose --env-file ./env.conf convert name: dockercomposetest services: web: image: webapp:123 networks: default: null networks: default: name: dockercomposetest_default 
user@laptop:~$ env $(cat ./env.conf | xargs) docker stack deploy --compose-file docker-compose.yml stack Creating service stack_web failed to create service stack_web: Error response from daemon: rpc error: code = InvalidArgument desc = ContainerSpec: "webapp:${VARIABLE_B}" is not a valid repository/tag

As you can see when using docker stack deploy it detects ${VARIABLE_A:-${VARIABLE_B}} is an environment variable that, because VARIABLE_A is not set, it should default to ${VARIABLE_B} however it does not resolve its value which is 123

Obviously, webapp does not exist, it's only an example, but the above error output should be this instead

user@laptop:~$ env $(cat ./env.conf | xargs) docker stack deploy --compose-file docker-compose.yml stack Creating service stack_web failed to create service stack_web: Error response from daemon: rpc error: code = InvalidArgument desc = ContainerSpec: "webapp:123" is not a valid repository/tag

Why does this happen? Is there any workarounds for this?

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3 Answers 3

Reset to default
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For reference see in moby docker stack deploy in 1.13 doesn't load .env file as docker-compose up does. Specifically Comment from kinghuang

"I have my developers use docker-compose config to pre-process Docker Compose projects before passing them to docker stack deploy. You can do this in one line with:

docker stack deploy -c <(docker-compose config) stack-name-here

That way, all Docker Compose features including .env processing are fully applied."

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  • I haven't tested this solution, but I'll mark it as valid since it looks way cleaner than what I ended up doing Commented Aug 27, 2023 at 11:58
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The workaround i ended up doing for docker stack deploy is using envsubst to replace env vars

user@laptop:~$ env $(cat ./env.conf | xargs) envsubst < ./docker-compose.yml | docker stack deploy --compose-file - stack

Documentation says that by using --compose-file - it takes the stdin as the docker compose file, so basically what this does is to first resolve all the variables in the docker-compose.yml then pass the result using a pipe to docker stack deploy

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0

Here is another nice way how you can overcome this problem. You have to create a ".env" file with all the variables you want to add to the environment for example: APP_NAME=Example . Then in your stack-compose.yml you can declare it like this:

version: "3.9" services: myservice: env_file: - .env

After this, you should run the following command:

docker stack config -c stack-compose.yml | docker stack deploy -c - mystackname

Which will insert the variables that you declared in the .env file in the stack_compose.yml like this:

version: "3.9" services: myservice: environment: APP_NAME: "Example"

In this link How to pass env variables in docker swarm stack

You will find a very good explanation of how to do this. I had the same problem and overcame it this way. Regards

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  • While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review Commented Feb 9, 2024 at 15:54
  • Hey @DaveM thanks for your comment. I improved my answer based on the link explanation. Regards Commented Feb 9, 2024 at 16:24

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